Relativistic effects in the variable-screening model

Abstract

The variable-screening model devised for a quantitative treatment of screening effects in slow (quasimolecular) ion-atom collisions is extended to include relativistic effects. Relativistic correction terms corresponding to a relative energy correction of second order in the electron velocity are incorporated into the effective molecular single-electron Hamiltonian. The model is applied to the calculation of relativistic molecular-orbital correlation diagrams for the quasimolecular systems Br + Br, Xe + Xe, and I + Au. A detailed comparison of our results with the results of relativistic calculations for (unscreened) one-electron systems and calculations based on self-consistent field methods is performed. The agreement with Dirac-Fock-Slater results is fairly good, and could be improved further by readjusting the values of the parameters in the atomic potentials used to construct the effective molecular potential.

Molecular-orbital study of late-fission times in deep-inelasticU238+

“…Hence, for later discussion, we define the following absolute times (/ =0 at nuclear contact between the 238 U projectile and 238 U target): t\, the deep-inelastic sticking time; t 2 , the time for the two U-like products to reach jRmin; he, the time at which a U-like product scissions; and ^3, the time at which the fission products, e.g., Pd + Pd for symmetric fission, reach a relative separation such that their \s<j MO energy still lies within -10 keV of Z?A:(U) [5]. With these definitions, emission of a Ulike K x ray followed by late fission occurs in the interval between t 2 and t 3 .…”

“…The method is related to that proposed by Gugelot [4] and, although not as detailed as the other methods, has the advantage that the information is obtained simply and is essentially free of nuclear models. We first discuss the experimental findings, then provide an interpretation using molecularorbital (MO) correlation diagrams for two-and threebody atomic systems [5][6][7]. Figure 1 sketches the experimental arrangement.…”

Molecular orbital model of atomic collisions

“…29 It is important to emphasize that the Rosenthal pseudocrossings can have no effect on electron promotion; instead, they only affect the relative subshell vacancy production. Nevertheless, this problem was largely unsolved until the advent of the quantitative calculations.55,56, 60 Larkins,55 on the basis of a correlation diagram constructed by a Hartree-Fock calculation on Ne-Ne, assumed that the Rosenthal pseudocrossing 3pc-3dc (see These results are shown in Figure 30. On the other hand, for asymmetric collisions, the new set of rules56 seems to be favored.…”

X rays from quasimolecules

“…To analyze two-collision MO x-ray cross sections, it is desirable to measure simultaneously MO x rays, projectile SA K x rays, and spectroscopic features of the projectile K x-ray spectra (Kaufmann et aL, 1973). Line shapes taken with bent-crystal spectrometers, line shifts (Greenberg et aL, 1977), or Ka to K(3 intensity ratios give information about the L and M shell populations which affect the projectile K x-ray decay rates in Eq.…”